Amber Reed Notes

Chapter 5:

Light : The cosmic Messenger

what is light?

-light from sun is called "white light" a blended mixture of all the spectrums
-sun emits electromagnetic energy
-shorter wave length has higher energy
-longer wave length has lower energy
-light is also known as electromagnetic radiation
-visible light that splits into rainbow of color is only a tiny part of the complete spectrum of light
-wave length is the distance between adjacent peaks and the frequency as the number of times that any piece of the rope moves up and down each second
-light can affect both electrically charged particles and magnets, light is an electromagnetic wave
-speed of light is about 300,000 km/second
-photons are particles of light
-light with waves lengths somewhat longer than red light is infrared because it lies beyond the red end of the rainbow
-radio waves are the longest waves
-the region near the border between infrared and radio wavs, where wave lengths range fro micrometers to millimeters, is sometimes called microwaves
-wavelength x frequency= speed of light=constant
-light with wavelengths somewhat shorter than blue light is called ultraviolet because it lies on the blue (violet) end of rainbow
-light with even shorter lengths is called X-rays
-the shortest wave lengths is gamma rays

What is Matter?

-protons and neutrons are found in the tiny nucleus at the center of the  atom
-electrical charge in a fundamental physical property that describes how strongly an object will interact with electromagnetic fields; total charge is always conserved just as energy is always conserved
-atomic number each chemical element contains a different number of protons in its nucleus
-atomic mass the combined number of protons and neutrons in an atom
-isotopes of a particular chemical element all have the same number of protons but different numbers of neutrons
-the number of different material substances is far greater than the number of chemical elements because atoms can combine to form molecules
-molecules consist of two or more atoms

How do light and matter interact?

-matter can emit,absorb,transmit or reflect light
-emission:  a light bulb emits visible light; the energy of the light comes from electrical potential energy supplied to the bulb (fusion)
-absorption:when you place your hand near an incandescent light bulb, your hand absorbs some of the light and this absorbed energy warms your hand (heat up matter)
-transmission:some forms of matter, such as glass or air transmit light which means allowing it to pass through ( general term for movement of E.M. through a medium)
-transparent objects transmit light
-opaque objects block (absorb)light
-reflection/scattering:light can bounce off matter,leading to  what we call reflection(when bouncing is all in the same general direction) or scattering (when the bouncing is more random)
-Three basic types of spectra:
-continuous
-emission line : a thin or low density cloud of gas emits light at specific wave lengths that depend on its composition and temp, producing a spectrum with bright emission lines
-absorption line :a cloud of gas between us an a light bulb can absorb light of specific wave lengths leaving dark absorption lines in the spectrum
-intensity: the light at each wave length in the spectrum
interactions between light and matter determine the appearance of everything around us


How does light tell us what things are made of?

-energy levels are possible energies of an atom
-electrons in atoms can have only particular amounts of energy and now other energies in between  

chemical fingerprints:
-each type of atom has unique set f energy levels
-each transition corresponds to a unique photon energy, frequency and wavelength
-downward transitions produce a unique pattern of emission lines
-because those atoms can absorb photons with those same energies,upward transitions produce a pattern of absorption lines at the same wave lengths
-each atom had a unique spectral fingerprint 
-observing the fingerprints n a spectrum tells us which kinds of atoms are present

thermal radiation
-nearly all large or dene objects emit thermal radiation,including stars, planets and you
-an objects thermal radiation spectrum depends on only one property its temperature


Properties of thermal radiation:
-hotter objects emit more light at al frequencies per unit area
-hotter objects emit photons with higher average energy

Reflected sunlight:continuous spectrum of visible light is like the sun's except that some of the blue light has been absorbed-the object must look red

How does light tell us the speed of distant object?
-the Doppler effect tells us how fast an object is moving toward or away form us. Spectral lines are shifted to shorter wave lengths (blueshift) for objects moving toward us and to longer wavelengths (a redshift) for objects moving away from us.

How so telescopes help us learn about the universe?

-Telescopes allows us to see fainter objects and to see more detail we can see with out eyes. Telescopes specialized to observe different wavelengths of light allow us to learn far more than we could form visible light alone. Light collecting area describes how much light telescope can collect,an angular resolution determines the amount of detail in the telescopic images 

Why do we put telescopes in space?

-Telescopes in space are above earth atmosphere and not subject to problems caused by light pollution,atmospheric distortion of light or the fact that most forms of light do not penetrate through the atmosphere to the ground.

How is technology revolutionizing astronomy?

-Technology makes it possible to build more powerful telescopes ad to enhance the capabilities of existing telescopes. Two key technologies are adaptive optics, which can overcome the distorting effects of earth's atmosphere, and interferometry, in which individual telescopes are linked in a way that allows the to obtain the angular resolution of much larger telescope



Amber Reed

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